Code shared from the Rust Playground

playground.rs

fn main() -> Result<(), Box<dyn std::fmt::Debug>> {
    let contents =
        std::fs::read_to_string("my.txt").map_err(|e| Box::new(e) as Box<dyn std::fmt::Debug>)?;
    let number = contents
        .parse::<i32>()
        .map_err(|e| Box::new(e) as Box<dyn std::fmt::Debug>)?;
    println!("Number is {}!", number);
    return Ok(());
}